Endometriosis is a major cause of severe pelvic pain, pain during menstruation, dyspareunia and infertility in women of child-bearing age with an estimated $22 billion cost of diagnosis and treatment in the U.S. The disease ordinarily regresses after menopause and is highly dependent on estrogen. Laparoscopic surgery provides temporary pain relief, but the recurrence rate is conservatively estimated to be 50% after five years. The benefits of drug treatment are also limited. For example, suppression of ovarian estrogen production by six months of gonadotropin-releasing hormone (GnRH) agonist therapy carries a significant risk of bone loss, is not obviously more effective than treatment with oral contraceptives, and also has a 50% or higher recurrence of symptoms within 5 years. Endometriotic lesions synthesize estrogen endogenously and this may be pathologically significant. Reports that aromatase inhibitors, which block the final step of estrogen synthesis, are effective in rare cases of post-menopausal endometriosis support this conclusion. But aromatase inhibitors are not used for treatment of endometriosis in pre-menopausal women because they stimulate ovarian cyst formation. Clearly, new medical therapies for endometriosis are desperately needed. We have identified small molecule antagonists to an orphan nuclear receptor that controls the major genes involved in de novo steroid hormone synthesis from cholesterol. Expression of this receptor is highly elevated in ectopic endometrial implants when compared to normal endometrium, and overexpression of this orphan receptor is strongly implicated as a driver of local estrogen biosynthesis. Receptor overexpression may regulate other aspects of endometriotic pathology, in addition to estrogen production, and orally bioavailable receptor antagonists represent a new therapeutic approach to directly target the endometriotic lesion. The objectives of this proposal are: (i) to demonstrate that proprietary receptor antagonists inhibit steroidogenic gene expression and estrogen synthesis in cultured endometriotic stromal cells;in parallel, we will measure steroid synthesis in human primary adrenal cultures, where the receptor is also expressed, to assess tissue specificity of receptor antagonists;(ii) to evaluate an alternative endpoint of therapeutic efficacy, receptor antagonist suppression of endometriotic cell growth and apoptosis in culture;and (iii) to synthesize antagonist ligands with improved potency (EC50 <10 nM) for the target cell assays. The same receptor is present in pituitary gonadotropes and the ovary and thus antagonists may also suppress gonadotropin hormone secretion and ovarian estrogen synthesis. Our long-term objective is to identify orally bioavailable drug candidates, to characterize effects on normal steroidogenesis in vivo, and to partner with a major pharmaceutical company for further preclinical and clinical development. PUBLIC HEALTH RELEVANCE: Endometriosis affects 6-10% of women of child-bearing age, and it is a leading cause of disability and pelvic pain in this age group. Of women treated for infertility, about 30% have endometriosis. In 1991-2, for example, 2.2% of hospital admissions in the U.S. were related to endometriosis with an average stay of 3.5 days. There is a major unmet need for new pharmacological treatments that can palliate the disease and delay recurrence after surgery. The proposed research will generate proof-of-principle data on antagonists to a previously unexplored drug target that is highly expressed in endometriosis and appears to be central to the pathophysiology of this debilitating disease.